|MadSci Network: Neuroscience|
Hola Ms. Campos, You're question is a good one. In fact, there are a few classical experiments on color that involve spinning tops. There are two fundamental things you have to know to understand the answer to this question. The first is the difference between "additive" color mixing and "subtractive" color mixing. The second thing is a few basic facts about the visual system (good thing I'm in optometry school right now!). First off, when we think about mixing colors, what we normally think about is subtractive color mixing. OK, to start, we see a rose as red because it's absorbing almost all other colors but red, and reflecting mostly the red. So if we mix red paint in with another color, the red paint is still absorbing everything but red. If you mix in yellow paint (which reflects mostly yellow), the red and yellow are each still absorbing the same colors they were respectively absorbing before they were mixed. The red paint absorbs yellow, and the yellow absorbs the red. Between them, they "subtract" most other colors out. But they both let a little orange reflect, so we perceive the paint as orange. Additive color mixing is a different kettle o' fish. If you shine a red light on the same spot as a green light, you don't get gray (which is what you'd get by mixing them as paints). You get something close to orange. Why this happens has to do with the wave nature of light and other complicated stuff we don't need to get into. Suffice to say, additive color mixing isn't something we usually think about. A TV screen works by additive color mixing, for instance, but we usually don't wonder how it works. There are many good web sites that let you do additive mixing to get a better idea how it works. Here's one; for more, just type in "additive color mixing" in your favorite search engine: Fun with additive colors Now, think about how many RPMs that top is doing. It's a lot. Our eyes can't follow something that fast. For instance, flourescent light bulbs are actually flickering, but it's occurring so fast that we can't see the individual flickers, but only a constant light. We know a movie is made up of individual frames, but if you play it fast enough, it appears like smooth motion. Our eyes and brains can't keep up with the separate images, so they fuse into a fluid image. The fancy term for this is "temporal summation," that is, adding up over time. Same for your top. We can't see individual points on the top, because it's spinning too fast. When it starts slowing down, you can start to see the individual circles again. Back to the top. What you can do is take a compass and draw concentric circles outward from the center of the top. Now imagine you hold a needle over the top in a certain place and set the top spinning without moving the needle. We also have to imagine that the top stays in the same place while spinning. Now, if you look at the part of the top under the tip of the needle, you can see that every point on a given circle is spinning under the point of the needle many many times in the span of a second. Your brain and eyes are too slow to see each point go by. Just like the flickering light or the movie, your brain adds together all the information. Because the top is going so fast, every point on the circle gets added up and perceived at the same time. So hopefully now you can see that all you have to do is figure out what colors are on each circle and add them together with an additive color mixer! You didn't describe the exact shape of the color wedges in the circles, but I imagine that on your inner circles you will find only red. The next circles out probably have some red points and some blue, which make violet. The next circles are probably blue, then a mix of red and yellow (orange), then plain yellow, then yellow with maybe some blue. The reason there is no green is that there is no single circle on the top that contains the right amounts of the three colors on your top to add together to make green. But you're not just limited to tops! Try the same thing with construction paper on anything that you can get to whirl rapidly (and safely), like a fan. Try it with different colors and see what you can get. Try it with different colors taking up more or less of the fan. You'll get some interesting results! If you have any more questions, email me at firstname.lastname@example.org. Oh yeah, I forgot to thank Dr. Arthur Bradley, a very smart scientist here at the IU School of Optometry who explained most of this to me. Good luck, Tom Stickel
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